The present invention is a grate in the shape of a grid for use in a combustion vessel. It is particularly useful in a fluidized bed in which the material combusted is non-uniform and subject either to agglomeration or to having tramp material entrained.
In incinerators, combustion chambers or fluidized bed reactor vessels, various means have been used for supporting the combustible material or the fluidized bed. The two major types of grates which are prevalent are bar grates and plate grates.
A bar grate is designed to allow air to flow up through the burning bed of material and to allow ash and tramp material to be removed from the bottom of the bed. The ash and tramp material, as well as bed material, pass through the spaces between the bars. This type of grate normally has an air manifold which distributes air to individual bars connected to the manifold. Each air bar has air nozzles for dispersing fluidizing air into the bed material.
A plate grate does not allow fluidized bed and/or tramp material to pass through the plate. Rather, the plate which is in the form of a flat or cone-shaped solid surface has air nozzles connected to perforations in it to expel air and maintain a fluidized bed above the grate. Air is supplied from an air box beneath the perforated plate or cone.
Both of these grates have certain disadvantages which can limit the operating time of a fluidized bed. The bar grate, despite having spaces between bars through which ash, tramp material and agglomerated material can fall, tends to accumulate material which is too large to pass through the gaps between adjacent bars. Thus, after a period of operation, the upper surface of the grid becomes covered by tramp material and fluidization of the bed decreases. The loss of fluidization creates a loss in the effectiveness of the unit.
In a plate grate system, a similar problem occurs to an even greater extent. There is no means by which tramp material or agglomerated bed material can be removed from the entire upper surface of the grate other than by shutting down the bed completely to remove such material.
The individual nozzles used in these systems account for a major portion of the cost of the grates. Elimination or simplification of the nozzles would have a significant effect on reducing the cost of the grate.